Rheological testing of resinous polymeric materials to measure properties such as melt flow rate, melt index and die swell involves many operations and must be performed consistently test after test in order to obtain reproducible data. These properties, in turn, are commonly used to assist in selecting polymer or grades thereof for use in particular applications such as monitoring polymer production processes, and establishing suitable process conditions for these polymers. It is desirable, therefore, to eliminate inconsistencies that are inevitable, due to individual-to-individual variations in technique or because of fatigue of an individual operation over a period of time.
Improving the precision of rheological properties of thermoplastic materials has long been the goal of those concerned with the testing of thermoplastic materials, particularly the melt flow rate and melt index properties.
U.S. Pat. No. 4,680,958 discloses an apparatus for the fast determination of the rheological properties of thermoplastic polymers. The apparatus disclosed in this patent is operable to raise and lower a test weight over a test cavity. However, the disclosed apparatus is not operable to load the sample in the test cavity and to clean the test cavity after the test.
U.S. Pat. No. 4,335,336 discloses a method and device for automatically and instantaneously computing and displaying with high precision the flow rate of thermoplastic samples run in an extrusion plastometer in accordance with ASTM Method D 1238-86. The method and device comprise using a microcomputer and related circuitry to monitor and control the measurement process and subsequently compute the resulting flow rate. The disclosed apparatus is not suggested for loading the sample into the test cavity or for cleaning the test cavity after the test.
A bulletin of Robotic Scientific, Inc., P.0. Box 11037, Spring, Tex. 77391-1037 labeled as a technical information bulletin disclosed a robotic instrument which automatically measures the flow rate of extruded polymers according to ASTM Standard Test Method D 1238-86. The instrument consists of two, automatic extrusion plastometers equipped with carousels holding up to twenty-four sample cartridges each, and uses replaceable cartridges and pistons which conform to the specifications of the ASTM Standard. The bulletin does not suggest cleaning of the test cavity or pistons after the test.
The melt flow rate or "melt index" of thermoplastics as determined by ASTM Method D 1238-86 (current edition approved Oct. 31, 1986 and published December 1986; originally published as D 1238-65T; incorporated herein by reference), or foreign counterparts, is generally employed as a specification or inspection property.
It is a goal of the automated flow rate machine of the present invention to provide automatic testing and subsequent cleaning of the test cavity and the pistons utilized in carrying out the test to provide high precision and high reproducibility in the test data.
As will be described in greater detail hereinafter, in a preferred embodiment the automated flow rate of the present invention utilizes automated devices to perform various functions, thereby to enable the machine to perform a complete test from loading a sample into a test cavity of a heating block for carrying out the test and for subsequent cleaning at the end of the test of the test cavity and the piston used to determine rheological properties of a thermoplastic such as melt flow rate.